Abstract:

This paper analyzes the structure and structural style of Dongpu sag basin, and concludes that the Paleogene basin of Dongpu sag has the structural characteristics of multi-fault, multi-convex and multi-sub-sag.The multi-convex and multi-sub-sag basin structure controls the sub-sag and the hydrocarbon, and forms the multi-convex and multi-sub-sag and multi-reservoir migration unit. The sedimentary period of the upper sub-member of the fourth member and the lower sub-member of the third member of Shahejie Formation is the early-strong fault depression period, and the transition from single fault wide basin to strong fault deep basin, with a humid climate, wide lake basin and deep water body, is a strong reduction environment, and the quality of hydrocarbon source rocks is excellent. The sedimentary period of the middle and upper sub-member of the third member of Shahejie Formation is more faulted period, with the lake basin becoming slow, highly segmented and medium water body. The hydrocarbon source rocks are concentrated and of general quality in the center of each depression.The sedimentary period of the second member of Shahejie Formation is a weak faulted period, with a continuous multi-depression pattern and an independent hydrocarbon generating unit at the beginning of accumulation. The source rocks are not developed in a dry climate, a small lake-shallow water type, and a shallow water body. In the eastern sag belt of the basin, the area with a large buried depth of the upper and lower sub-member of the forth member of Shahejie Formation enters the threshold of hydrocarbon generation, and the source rocks mature rapidly. During the Dongying movement, the reservoir is mainly regulated, and the oil and gas generated in the early stage is transformed by small faults to form many small fault blocks. From late sedimentary period of Minghuazheng Formation to present, the fault activity is weakened, the formation thickness compensation in the sag zone continues to generate hydrocarbon, and the hydrocarbon accumulation is mainly in the lower part.

Key words: Dongpu sag, more convex and hollow, basin structure, tectonic evolution, hydrocarbon accumulation